As is known in the art, efficient antennas in the high-frequency range are large. A typical antenna length can be in the range of about λ/2 to λ/4, where λ is the wavelength of the carrier frequency. For example, the wavelength at 1 Megahertz (MHz) is 300 meters and at 10 MHz is 30 meters. These antennas are too long to be practical for many applications, especially for on-the-move operations requiring portable receivers, such as those carried in backpacks or mounted on vehicles.
As is also known in the art, active antennas reduce the size of the antenna element by using an amplifier to boost input signals. For example, a typical size of an active antenna is 18 inches, which is far less than other antenna designs. A problem with active antennas, however, is that the amplifier increases noise along with the desired target signal. Further, the amplifier can reduce the signal-to-noise ratio of the communications signal at the amplifier output.